The goal of this research is to develop a post-implantation annealing process in silicon carbide (SiC). Due to the low diffusivities of dopants in SiC, even at temperatures in excess of 2000°C, diffusion is not a suitable process to achieve selective, planar doping. Ion implantation is therefore the most suitable means for achieving selective doping in SiC crystals. The strong covalent bonding in SiC requires that selective doping be performed via high-energy ion implantation. As a consequence of the high ion energy and flux, there is considerable lattice damage to the crystal surface. To repair the damage caused by the implantation, as well as to electrically activate the dopants, it is important to perform post-implantation thermal annealing at temperatures greater than 1600°C. However annealing at such high temperatures decomposes the SiC crystal surface due to the selective out-diffusion of Si causing surface morphology degradation. In this research two processes, both using a silane-based SiC CVD reactor, have been realized to minimize the evaporation of Si. This is accomplished by providing Si overpressure above the wafer surface during annealing thus suppressing the evaporation of Si from the lattice. Post-implantation anneals were performed in both hot-wall and cold-wall silane-based chemical vapor deposition (CVD) reactors. For each process temperature developed, silane was added to a stream of Ar in such a concentration such that the suppression of step-bunching, a well known phenomenon caused by the evaporation of Si at the surface, was achieved. The surfaces were studied after annealing via plan-view secondary electron microscopy (SEM) and atomic force microscopy (AFM). The resulting surface morphology was found to be both step-free and smooth. Results of the annealing process developed, the surface characterization performed and electrical data relating to the dopant activation and implanted region conductivity are presented.

Polycrystalline CdS/CdTe thin film solar cells are among the leading candidates for low-cost, large scale terrestrial photovoltaic applications. CdTe has a high absorption coefficient and it can absorb the radiant energy within less than 2 µm of thickness. This makes it suitable for thin film applications. CdTe has a band gap of 1.45 eV at room temperature, which is nearly optimum for photovoltaic conversion efficiency under the AM 1.5 solar spectrum. The theoretical maximum efficiency for CdTe solar cells is 29%. However, to-date the experimental value is in the 16 % range. In most cases CdTe cells are subjected to a post-growth heat treatment which involves annealing in the presence of CdCl2. The treatment results in significant increases in conversion efficiency (η) and all three solar cell parameters Voc, FF, and Jsc. In this work, several variations of the CdCl2 treatment were used on more than 100 samples to investigate their effects on the solar cell parameters. A vapor CdCl2 method was applied for the treatment with various source temperatures, substrate temperatures, and treatment times. The cells were characterized by dark and light J-V and spectral response (SR) measurements.

Les zirconates titanates de plomb (PZT) suscitent un intérêt considérable pour plusieurs applications industrielles, au regard de leurs excellentes propriétés piézoélectriques et électromécaniques. Le contexte actuel de l’innovation technologique est la miniaturisation et l’allègement des produits ; c’est pour cette raison que de nombreuses études sont menées depuis une vingtaine d’années sur les techniques et les procédés de synthèse de ces matériaux piézoélectriques sous forme de couches minces tout en garantissant une fiabilité accrue. Dans ce contexte, l’étude menée dans le cadre de cette thèse, a visé l’optimisation du procédé d’élaboration de films minces piézoélectriques de PZT par pulvérisation cathodique magnétron en mode DC et en mode Rf, en vue d’obtenir des capteurs d’efforts piézoélectriques. La synthèse in situ et la cristallisation ex-situ des films élaborés, par recuit classique (CFA) ou recuit rapide (RTA) confirme une structure pérovskite du PZT, complétées par une série de caractérisations morphologiques et structurales. Les domaines ferroélectriques à l’origine des propriétés piézoélectriques sont correctement visualisés par PFM et le calcul du coefficient piézoélectrique d33 des couches synthétisées sur des substrats métalliques, est réalisé par interféromètre laser. En parallèle, une approche expérimentale est menée sur l’évolution des performances piézoélectriques des films de PZT d’une part en fonction du mode d’élaboration et d’autre part en fonction de la texturation des couches, assurée par des traitements thermiques de cristallisation. / Recently, PZTs thin films have been spotlighted for various applications owing to their excellent piezoelectric and electromechanical properties. Most of the existing coating methods have been explored for the deposition of PZT. In this work, amorphous Pb(ZrxTi1-x)O3 (PZT) thin films were prepared by pulsed DC and RF magnetron sputtering in order to device a piezoelectric force sensors. The structure of a perovskite phase of PZT thin films was successfully characterized and morphological characterizations were investigated. Ferroelectrics properties of PZT thin films were determined using Piezoresponse Force Atomic technique (PFM) while the functional response of the films was characterized by measurements of piezoelectric d33 coefficients. Additionally, the coating processes and the crystallization behavior at different temperatures, of amorphous PZT thin films during either conventional furnace annealing (CFA) or rapid thermal annealing (RTA) were studied to understand the evolution of piezoelectric properties of films.

Abstract not available

There are many real world assignment, scheduling and planning tasks which can be classified as combinatorial optimisation problems (COPs). These are usually formulated as a mathematical problem of minimising or maximising some cost function subject to a number of constraints. Usually, such problems are NP hard, and thus, whilst it is possible to find exact solutions to specific problems, in general only approximate solutions can be found. There are many algorithms that have been proposed for finding approximate solutions to COPs, ranging from special purpose heuristics to general search meta-heuristics such as simulated annealing and tabu search. General meta-heuristic algorithms like simulated annealing have been applied to a wide range of problems. In most cases, the designer must choose an appropriate data structure and a set of local operators that define a search neighbourhood. The variability in representation techniques, and suitable neighbourhood transition operators, has meant that it is usually necessary to develop new code for each problem. Toolkits like the one developed by Ingber's Adaptive Simulated Annealing (Ingber 1993, 1996) have been applied to assist rapid prototyping of simulated annealing codes, however, these still require the development of new programs for each type of problem. There have been very few attempts to develop a general meta-heuristic solver, with the notable exception being Connolly's General Purpose Simulated Annealing (Connolly 1992). In this research, a general meta-heuristic based system is presented that is suitable for a wide range of COPs. The main goal of this work is to build an environment in which it is possible to specify a range of COPs using an algebraic formulation, and to produce a tailored solver automatically. This removes the need for the development of specific software, allowing very rapid prototyping. Similar techniques have been available for linear programming based solvers for some years in the form of the GAMS (General Algebraic Modelling System) (Brooke, Kendrick, Meeraus and Raman 1997) and AMPL (Fourer, Gay and Kernighan 1993) interfaces. The new system is based on a novel linked list data structure rather than the more conventional vector notation due to the natural mapping between COPS and lists. In addition, the modelling system is found to be very suitable for processing by meta-heuristic search algorithms as it allows the direct application of common local search operators. A general solver is built that is based on the linked list modelling system. This system is capable of using meta-heuristic search engines such as greedy search, tabu search and simulated annealing. A number of implementation issues such as generating initial solutions, choosing and invoking appropriate local search transition operators and producing suitable incremental cost expressions, are considered. As such, the system can been seen as a good test-bench for model prototypers and those who wish to test various meta-heuristic implementations in a standard way. However, it is not meant as a replacement or substitute for efficient special purpose search algorithms. The solver shows good performance on a wide range of problems, frequently reaching the optimal and best-known solutions. Where this is not the case, solutions within a few percent deviation are produced. Performance is dependent on the chosen transition operators and the frequency with which each is applied. To a lesser extent, the performance of this implementation is influenced by runtime parameters of the meta-heuristic search engine.

Thin-film solar cells on glass substrates are likely to have a bright future due to the potentially low costs and the short energy payback times. Polycrystalline silicon (poly-Si, grain size &gt 1 pm) has the advantage of being non-toxic, abundant, and long-term stable. Glass as a substrate, however, limits the processing temperatures to ~600??C for longer process steps. Films with large grain size can be achieved by solid phase crystallisation (SPC), and especially by solid phase epitaxy (SPE) on seed layers, using amorphous silicon deposited at low temperatures as a precursor film. With SPC and SPE, the amorphous silicon film is typically crystallised at ~600??C over hours. During this anneal at atmospheric pressure -depending on the properties of the amorphous silicon film- ambient gas can percolate the film and can negatively affect the crystallisation. In this work, a high-vacuum anneal chamber was designed and built to allow the in-situ crystallisation of amorphous silicon films deposited on glass in a PECVD cluster tool. An important aspect of the design was the comfortable and safe operation of the vacuum anneal chamber to enable unattended operation. This was realised by means of a state-of-the-art, programmable temperature controller and a control circuit design that incorporates various safety interlocks. The chamber interior was optimised such that a temperature uniformity of 2-3K across the sample area was achieved. The chamber was calibrated and tested, and SPC and SPE samples were successfully crystallised. In initial SPC crystallisation experiments with solar cell structures, after post-deposition treatments, a 1 -sun open-circuit voltage of 465 mV was obtained, similar to furnace-annealed samples. In initial experiments with SPE solar cell structures, difficulties regarding the characterisation of the unmetallised solar cells with the quasi-steady-state open-circuit voltage method (QSSVOC) were encountered after post-deposition hydrogen treatment. A possible explanation for these difficulties is the contact formation with the metal probes. Furthermore, limiting factors of the QSSVOC method for the characterisation of unmetallised cells with high contact resistance values were investigated and, additionally, the accuracyof the QSSVOC setup was improved in the low light intensity range.

The effect of initial microstructures of an 0.05 wt.% C low carbon steel, acicular ferrite (AF), Bainite (B), polygonal ferrite (PF), fine polygonal ferrite (FPF), and a microstructure produced by direct strip casting (DSC) (termed SC), on the deformation and recrystallization behaviour of cold rolled low carbon (LC) steel, was investigated. The initially prepared samples with the initial microstructures were cold rolled to 50, 70 and 90% reductions, then annealed isothermally in the temperature range 580 ??? 680 oC. The microstructures and textures produced by deformation and annealing were studied by optical microscopy, XRD, TEM, SEM and EBSD. The initial microstructures were characterized mainly by optical microscopy and EBSD. Using EBSD, the ferrite grain size of the AF, B and SC samples was considerably larger than that found by optical microscopy with a large fraction of low angle grain boundaries (LAGBs) observed within prior austenite grains. All samples exhibited a very weak texture close to random. After cold rolling, the microstructures of AF and SC contained shear bands with PF and FPF generating deformation bands. For AF and SC, the pearlite phase was more extensively elongated in rolling direction compared with PF and FPF. After 90% cold rolling reduction, PF, FPF and SC consist mainly of the texture component and AF and B . It was found that FPF recrystallized most rapidly followed by B, PF and AF with SC recrystallizing orders of magnitude more slowly due to the solution drag caused by its uniformly distributed higher Mn content. Very strong (???-fibre) texture was generated in cold rolled PF followed by FPF, with AF, SC and B generating very weak textures. The texture evolution during annealing 90% reduction PF was examined in further detail. The behaviour of nucleation and grain growth provides strong evidence of orientated nucleation as the dominant factor for CRA texture development in this material.

Group-III-nitride semiconductors (GaN, InGaN, and AlGaN) are important for the fabrication of a range of optoelectronic devices (such as blue-green light emitting diodes, laser diodes, and UV detectors) as well as devices for high-temperature/high-power electronics. In the fabrication of these devices, ion bombardment represents a very attractive technological tool. However, a successful application of ion implantation depends on an understanding of the effects of radiation damage. Hence, this thesis explores a number of fundamental aspects of radiation effects in wurtzite III-nitrides. Emphasis is given to an understanding of (i) the evolution of defect structures in III-nitrides during ion irradiation and (ii) the influence of ion bombardment on structural, mechanical, optical, and electrical properties of these materials. ¶ Structural characteristics of GaN bombarded with keV ions are studied by Rutherford backscattering/channeling (RBS/C) spectrometry and transmission electron microscopy (TEM). Results show that strong dynamic annealing leads to a complex dependence of the damage buildup on ion species with preferential surface disordering. Such preferential surface disordering is due to the formation of surface amorphous layers, attributed to the trapping of mobile point defects by the GaN surface. Planar defects are formed for a wide range of implant conditions during bombardment. For some irradiation regimes, bulk disorder saturates below the amorphization level, and, with increasing ion dose, amorphization proceeds layer-by-layer only from the GaN surface. In the case of light ions, chemical effects of implanted species can strongly affect damage buildup. For heavier ions, an increase in the density of collision cascades strongly increases the level of stable implantation-produced lattice disorder. Physical mechanisms of surface and bulk amorphization and various defect interaction processes in GaN are discussed. ¶ Structural studies by RBS/C, TEM, and atomic force microscopy (AFM) reveal anomalous swelling of implanted regions as a result of the formation of a porous structure of amorphous GaN. Results suggest that such a porous structure consists of N$_{2}$ gas bubbles embedded into a highly N-deficient amorphous GaN matrix. The evolution of the porous structure appears to be a result of stoichiometric imbalance, where N- and Ga-rich regions are produced by ion bombardment. Prior to amorphization, ion bombardment does not produce a porous structure due to efficient dynamic annealing in the crystalline phase. ¶ The influence of In and Al content on the accumulation of structural damage in InGaN and AlGaN under heavy-ion bombardment is studied by RBS/C and TEM. Results show that an increase in In concentration strongly suppresses dynamic annealing processes, while an increase in Al content dramatically enhances dynamic annealing. Lattice amorphization in AlN is not observed even for very large doses of keV heavy ions at -196 C. In contrast to the case of GaN, no preferential surface disordering is observed in InGaN, AlGaN, and AlN. Similar implantation-produced defect structures are revealed by TEM in GaN, InGaN, AlGaN, and AlN. ¶ The deformation behavior of GaN modified by ion bombardment is studied by spherical nanoindentation. Results show that implantation disorder significantly changes the mechanical properties of GaN. In particular, amorphous GaN exhibits plastic deformation even for very low loads with dramatically reduced values of hardness and Young's modulus compared to the values of as-grown GaN. Moreover, implantation-produced defects in crystalline GaN suppress the plastic component of deformation. ¶ The influence of ion-beam-produced lattice defects as well as a range of implanted species on the luminescence properties of GaN is studied by cathodoluminescence (CL). Results indicate that intrinsic lattice defects mainly act as nonradiative recombination centers and do not give rise to yellow luminescence (YL). Even relatively low dose keV light-ion bombardment results in a dramatic quenching of visible CL emission. Postimplantation annealing at temperatures up to 1050 C generally causes a partial recovery of measured CL intensities. However, CL depth profiles indicate that, in most cases, such a recovery results from CL emission from virgin GaN, beyond the implanted layer, due to a reduction in the extent of light absorption within the implanted layer. Experimental data also shows that H, C, and O are involved in the formation of YL. The chemical origin of YL is discussed based on experimental data. ¶ Finally, the evolution of sheet resistance of GaN epilayers irradiated with MeV light ions is studied {\it in-situ}. Results show that the threshold dose of electrical isolation linearly depends on the original free electron concentration and is inversely proportional to the number of atomic displacements produced by the ion beam. Furthermore, such isolation is stable to rapid thermal annealing at temperatures up to 900 C. Results also show that both implantation temperature and ion beam flux can affect the process of electrical isolation. This behavior is consistent with significant dynamic annealing, which suggests a scenario where the centers responsible for electrical isolation are defect clusters and/or antisite-related defects. A qualitative model is proposed to explain temperature and flux effects. ¶ The work presented in this thesis has resulted in the identification and understanding of a number of both fundamental and technologically important ion-beam processes in III-nitrides. Most of the phenomena investigated are related to the nature and effects of implantation damage, such as lattice amorphization, formation of planar defects, preferential surface disordering, porosity, decomposition, and quenching of CL. These effects are often technologically undesirable, and the work of this thesis has indicated, in some cases, how such effects can be minimized or controlled. However, the thesis has also investigated one example where irradiation-produced defects can be successfully applied for a technological benefit, namely for electrical isolation of GaN-based devices. Finally, results of this thesis will clearly stimulate further research both to probe some of the mechanisms for unusual ion-induced effects and also to develop processes to avoid or repair unwanted lattice damage produced by ion bombardment.

The present thesis is a study of the evolution of defect states in devices based on wide bandgap semiconductors. The attention has been focused on light-emitting diodes based on GaN and Schottky diodes based on SiC, these latter a basic structure for the fabrication of high-power rectifiers and ionising particle detectors. In both cases, we studied the defects and their electronic properties by means of the following experimental techniques: current-voltage (I-V) measurements, in order to investigate the effect of imperfections on the transport properties of the material/device; capacitance-voltage (C-V) measurements, yielding the profile of concentration of charge carriers, and giving information on the influence of defects on this concentration; deep level transient spectroscopy (DLTS), a technique allowing for the identification and characterization of defect-originated electron levels in the gap. I also employed techniques, such as photocurrent spectroscopy (PC), allowing for the characterization of light absorption by the material and/or device versus varying photon energy. In both cases of SiC and GaN, the defect characterization was always interpreted in the framework of its influence on device operation. In the analysed LEDs the defect evolution was connected to the evolution of quantum efficiency, and in the SiC diodes we studied the effects of defect introduction on the charge collection efficiency (CCE) and on the leakage current of the device. Furthermore, for the interpretation of photocurrent spectra, I developed a model describing the generation of photocurrent considering the dispersion relations for the absorption coefficient and refractive index in the various device layers, as well as the internal reflection, transmission and interference phenomena involving the optical field within the device. The research yielded various interesting results: I detected many deep levels introduced by proton- and electron-irradiation in SiC. From the study of their annealing behaviour I concluded that one of these levels is related to a particular lattice defect, the carbon interstitial. By means of the analysis of the introduction rates of the levels and comparisons between proton and electron irradiation, I was able to distinguish between deep levels related to simple intrinsic defects and to defect complexes. In the case of the GaN LED, I found that the evolution of several independent properties are strongly correlated, meaning that a single degradation mechanism is responsible for the observed changes. In particular, I concluded that the degradation of the light emission intensity is due to the generation of defects in the active region of the device.

<p>Today electronics becomes more and more complex and to keep low costs and power consumption, both digital and analog parts are implemented on the same chip. The degree of automization for the digital parts have increased fast and is high, but for the analog parts this has not come through. This have created a big gap between the degrees of automization for the two parts and makes the analog parts the bottleneck in electronics develop. </p><p>Research is ongoing at Electronics systems group at Linköping University target the increase of design automization for analog circuits. An optimizationbased approach for device sizing is developed and for this a good optimization method is needed which can find good solutions and meet the specification parameters. </p><p>This report contains an evaluation of the optimization method Simulated Annealing. Many test runs have been made to find out good control parameters, both for Adaptiv Simulated Annealing (ASA) and a standard Simulated Annealing method. The result is discussed and all the data is in the enclosures. A popular science and mathematical description is given for Simulated Annealing as well.</p>